Page 679 - Cardiac Nursing

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CHAPTER
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P P P P Pacemakers and Implantable Defibrillators*
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Carol Jacobson / Donna Gerity
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Ar Arrhythmia device therapy is becoming more complex with every y not capable of increaasing its rate appropriately inn responsse to thhe
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advance in technology, requiring clinicians to have more knowl- body’s need for increased cardiac output (chronotropic incompe-
edge and greater responsibilities than ever before. Early pace- tence). Dual-chamber pacemaker therapy can improve stroke vol-
makers were single-chamber devices designed to pace only in the ume in patients with LV dysfunction, hypertrophic cardiomyopa-
ventricle, and the only programmable parameters were pacing thy, or dilated cardiomyopathy by ensuring AV synchrony and
4,5
rate and output. With the introduction of dual-chamber pace- providing optimal AV intervals to enhance ventricular filling.
makers with the capability of pacing the atria and the ventricles, Cardiac resynchronization therapy (CRT) with biventricular pac-
the number of programmable parameters increased dramatically. ing improves septal wall motion, mitral valve function, and the
Rate-responsive pacemakers came next and are capable of in- dynamics of LV contraction in patients with severe HF or dilated
4–11
creasing the pacing rate in response to the body’s need for in- cardiomyopathy. The use of pacemaker therapy to prevent
creased cardiac output. Antitachycardia devices were developed atrial fibrillation is an area of intense interest and investigation
12–18
to terminate supraventricular and ventricular tachyarrhythmias and has proven successful in many patients. Other indica-
using pacing techniques, cardioversion, or defibrillation. Most re- tions for cardiac pacing include hypersensitive carotid sinus syn-
cently, the development of biventricular pacing capability allows drome, neurocardiogenic syncope (vasovagal syncope), long QT
1–4,19
for pacing to improve hemodynamics and left ventricular (LV) syndrome, and sleep apnea.
function in patients with heart failure (HF) and cardiomyopathy. The American College of Cardiology (ACC), American Heart
There have been tremendous advances in technology of devices Association (AHA), and Heart Rhythm Society (HRS) task force
for both bradycardia and antitachycardia therapy in recent years, on practice guidelines recently updated the guidelines for implan-
1
with even more complex devices coming in the future. Given the tation of pacemakers and antiarrhythmia devices. Display 28-1
number of companies in the arrhythmia device market and the lists the indications for permanent pacemaker implantation in se-
increasing complexity of the devices themselves, it has become lected clinical settings.
very difficult for clinicians to stay abreast of device features and Temporary pacing is indicated to treat symptomatic bradycar-
function. The goal of this chapter is to present generic concepts dia after AMI or cardiac surgery, or when associated with hyper-
of pacemaker and implantable defibrillator functions to provide kalemia or drug toxicity; bradycardia-dependent ventricular
a basic knowledge background upon which cardiac nurses can tachycardia (VT); before permanent pacemaker implantation in
build to enhance their understanding of arrhythmia management symptomatic patients; and in reversible conditions that will not
devices. likely result in the need for permanent pacing, such as bacterial
endocarditis, Lyme disease, or cardiac trauma. 20,21 Temporary
pacing in acute myocardial infarction (MI) is still controversial.
Indications for Pacing
Inferior MI results in intranodal block that is usually benign and
Pacemakers were originally designed to treat disorders of impulse temporary and requires pacing only if it results in symptomatic
initiation or impulse conduction resulting in symptomatic brady- bradycardia or bradycardia-dependent VT. When atrioventricular
cardia. Symptomatic bradycardia is a term used to define a brady- (AV) block occurs in anterior MI, it is usually infranodal, involves
cardia that is directly responsible for symptoms such as syncope, a large amount of myocardium, and is often symptomatic. Sec-
near syncope, transient dizziness, or light-headedness, and confu- ond- or third-degree AV block associated with anterior MI and
sion resulting from cerebral hypoperfusion caused by slow heart bundle-branch block usually requires temporary pacing, but the
1
rate. Other symptoms such as fatigue, exercise intolerance, HF, mortality rate is high because of LV dysfunction secondary to the
dyspnea, and hypotension can also result from bradycardia. large infarction rather than to the conduction disturbance. Pro-
Symptomatic bradycardia can be caused by sinus node dysfunc- phylactic temporary pacing is often performed in the presence of
tion or by conduction failure in or below the AV node. Sinus node new right bundle-branch block (RBBB) with either anterior or
dysfunction is the most common indication for permanent pac- posterior hemiblock, in left bundle-branch block (LBBB) with
ing, followed by AV node dysfunction. 2,3 first-degree AV block, and in alternating right and LBBB.
Temporary pacing is often used after cardiac surgery to prevent
or treat symptomatic bradycardia and is sometimes used prophy-
lactically in high risk patients during cardiac catheterization, oror
lactically in high - risk patients during car diac catheterization
*Carol Jacobson wrote the section on pacemakers. Donna Gerity wrote the with electrical or chemical cardioversion. Overdrive atrial pacing
section on implantable defibrillators.
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